Initial commit: pwweb - PipeWire WebUI

C++ backend with SSE streaming (reuses qpwgraph PipeWire callbacks).
Svelte frontend with custom SVG canvas for port-level connections.

Features:
- Live PipeWire graph via SSE
- Drag output->input port to connect
- Double-click or select+Delete to disconnect
- Node positions saved to localStorage
- Pan (drag bg) and zoom (scroll)
- Port type coloring (audio=green, midi=red, video=blue)

src/main.cpp

@@ -0,0 +1,69 @@
+#include "graph_engine.h"
+#include "web_server.h"
+
+#include <csignal>
+#include <cstdio>
+#include <cstdlib>
+#include <unistd.h>
+#include <atomic>
+
+static std::atomic<bool> g_running(true);
+
+static void signal_handler(int sig) {
+    g_running = false;
+    fprintf(stderr, "\npwweb: caught signal %d, shutting down...\n", sig);
+}
+
+int main(int argc, char *argv[]) {
+    int port = 9876;
+
+    // Parse optional port argument
+    if (argc > 1) {
+        port = atoi(argv[1]);
+        if (port <= 0 || port > 65535) {
+            fprintf(stderr, "usage: pwweb [port]\n");
+            return 1;
+        }
+    }
+
+    signal(SIGINT, signal_handler);
+    signal(SIGTERM, signal_handler);
+
+    pwgraph::GraphEngine engine;
+
+    fprintf(stderr, "pwweb: connecting to PipeWire...\n");
+    if (!engine.open()) {
+        fprintf(stderr, "pwweb: failed to connect to PipeWire.\n");
+        fprintf(stderr, "  Make sure XDG_RUNTIME_DIR is set: export XDG_RUNTIME_DIR=/run/user/$(id -u)\n");
+        return 1;
+    }
+
+    pwgraph::WebServer server(engine, port);
+
+    // Wire change notifications to broadcast
+    engine.setOnChange([&server]() {
+        server.broadcastGraph();
+    });
+
+    if (!server.start()) {
+        fprintf(stderr, "pwweb: failed to start web server on port %d\n", port);
+        engine.close();
+        return 1;
+    }
+
+    fprintf(stderr, "pwweb: server running at http://localhost:%d\n", port);
+    fprintf(stderr, "pwweb: API at http://localhost:%d/api/graph\n", port);
+    fprintf(stderr, "pwweb: press Ctrl+C to stop\n");
+
+    // Main loop — just wait for shutdown signal
+    while (g_running) {
+        std::this_thread::sleep_for(std::chrono::milliseconds(200));
+    }
+
+    fprintf(stderr, "pwweb: shutting down...\n");
+    server.stop();
+    engine.close();
+
+    fprintf(stderr, "pwweb: goodbye.\n");
+    return 0;
+}